1. Field of the Invention
The present invention relates generally to a cooling device useful for reducing the total injection molding cycle time of an injection molded tube, and more particularly to applying cooling to areas of a preform that are not in direct contact with the water cooled inside surface of a take out tube.
2. Statement of the Prior Art
The manufacture of hot-fill polyethylene terephthalate (PET) containers employs an initial step of forming a parison or preform by an injection molding process. Performs are generally in the shape of a hollow cylinder closed at one end and tapering to form an open end, known as a finish, that can have a diameter that is narrower than the diameter of the closed end. Performs having an open end that is narrower than a closed end are known as reverse taper style performs. To form a reverse taper perform, molten plastic is injected into a mold formed by a cavity and a core and partially cooled before being ejected from the mold. Typically, the preform is only in the mold cavity long enough to form an inner skin and an outer skin. Once the preform is hard enough to be ejected from the mold, the preform is taken off of the core and ejected into a take out tube for additional cooling. Using a take out tube greatly reduces the injection molding cycle time because the preforms do not remain in the mold for an extended length of time.
Conventional take out tubes consist of a straight right cylinder having internal water cooling channels designed to cool the inside walls of the take out tube, and hence the outer surface of the preform that makes intimate contact with the inside walls of the take out tube. However, conventional take out tubes are not effective in cooling reverse taper style preforms because they fail to make intimate contact with the entire length of the preform. This failure to cool the entire length of the preform causes an increase in the molding injection cycle time because more time is required to cool those portions of the preform that do not make intimate contact with the inside walls of the take out tube. Thus what is needed is a take out tube that can cool the entire length of a reverse taper style preform.
Many attempts have been made in the past to improve post-mold cooling systems. However, these attempts have not resulted in a substantial reduction of the molding injection cycle time. For example, U.S. Pat. No. 4,382,905 to Valyi discloses a means for cooling a preform by cooling the walls of a mold that make contact with the preform. The problem with this approach is that the apparatus only cools the portion of the preform that makes direct contact with the cooled walls of the mold. Furthermore, this approach does not disclose cooling the preform outside the mold, which results in an increased injection molding cycle time. Additionally, U.S. Pat. Nos. 5,176,871 and 5,232,715 disclose cooling a preform by blowing air around the preform. The principle problem with the apparatus and method shown in these patents is that the preform is retained in the mold core and this retention significantly increases injection molding cycle time. Thus, a take out tube that cools the entire length of the perform, particularly a reverse taper perform represents a solution to a long standing problem in the art. Specifically, such a take out tube can reduce injection molding cycle time for reverse taper performs.